The broad long-term goal of the project is to extend our knowledge of the temporal properties of sensory systems through an experimental study of vibrotactile temporal summation. By measuring psychophysical thresholds for detecting sinusoidal stimuli presented to the glabrous skin of the hand, the basic mechanisms of temporal integration should reveal themselves. The objective is to experimentally isolate the two possible fundamental mechanisms, probably summation and neural integration responsible for temporal summation in all sensory systems, and to define the conditions under which they operate in vibrotaction. By measuring psychophysical thresholds for detecting single and multiple-pulse stimuli when the level of and spectral characteristics of external background noise are manipulated it will be possible to test the hypothesis that probably summation in a sensory system requires a sufficient level of either internal or external noise so as to introduce a substantial amount of variability in the neural responses of the system, to repeated presentation of the same stimulus. By measuring thresholds for detecting multiple pulses separated by noise designed to disrupt the persistence of neural activity that could occur after termination of a stimulus, it will be possible to test the hypothesis that neural persistence is essential for the operation of the mechanism of neural integration. Through the use of a method of selective adaptation it will be possible to measure temporal summation over a range of stimulus frequencies from 20 to 540 Hz. The results will test Zwislocki's (1960) hypothesis, proposed to account for temporal summation in hearing, that individual cycles in a sinusoidal stimulus can serve as individual stimulus events in neural integration. By correlating cycles in a sinusoidal can serve as individual stimulus events in neural integration. By correlating measures of temporal summation, temporal gap detection and forward masking it will be possible to determine whether neural persistence, when necessary for temporal summation, reduces temporal acuity and disrupts the persistence, when necessary for temporal summation, reduces temporal acuity and disrupts the detectability of a signal presented after the termination of a masking stimulus.